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Encyclopedia > Thalamus
Brain: Thalamus
MRI cross-section of human brain, with thalamus marked.
Scheme showing the course of the fibers of the lemniscus; medial lemniscus in blue, lateral in red.
Latin thalamus dorsalis
Gray's subject #189 808
NeuroNames hier-283
MeSH Thalamus


The thalamus (from Greek θάλαμος = bedroom, chamber, IPA= /ˈθæləməs/) is a pair and symmetric part of the brain. It constitutes the main part of the diencephalon. Image File history File links Download high resolution version (860x860, 70 KB) Summary This is Image:Brian chrischan. ... The mri are a fictional alien species in the Faded Sun Trilogy of C.J. Cherryh. ... Image File history File links Gray713. ... This article needs to be wikified. ... The medial lemniscus, also known as Reils band or Reils ribbon, is a pathway in the brainstem that carries sensory information from the gracile and cuneate nuclei to the thalamus. ... The lateral lemniscus is a tract of axons in the brainstem that carries information about sound from the cochlear nucleus to various brainstem nuclei and ultimately the contralateral inferior colliculus of the midbrain. ... Latin is an ancient Indo-European language originally spoken in Latium, the region immediately surrounding Rome. ... NeuroNames is a system of nomenclature for the brain and related structures. ... Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ... The diencephalon is the region of the brain that includes the epithalamus, thalamus, and hypothalamus. ...

Contents

Location and topography

In the caudal (tail) to oral (mouth) sequence of neuromeres, the diencephalon is located between the mesencephalon (cerebral peduncule, belonging to the brain stem) and the telencephalon. The diencephalon includes also the dorsally located epithalamus (essentially the habenula and annexes) and the perithalamus (prethalamus formerly described as ventral thalamus) containing the zona incerta and the "reticulate nucleus" (not the reticular, term of confusion). Due to their different ontogenetic origins, the epithalamus and the perithalamus are formally distinguished from the thalamus proper. Neuromeres are transient segments during the early development of the human brain. ... In biological anatomy, the mesencephalon (or midbrain) is the middle of three vesicles that arise from the neural tube that forms the brain of developing animals. ... The cerebral peduncle, by most classifications, is everything in the mesencephalon except the tectum. ... Mostly enveloped by the cerebrum and cerebellum (blue), the visible part of brainstem is shown in black. ... The diencephalon is the region of the brain that includes the epithalamus, thalamus, and hypothalamus. ... The epithalamus is a dorsal posterior segment of the diencephalon (a segment in the middle of the brain also containing the hypothalamus and the thalamus) which includes the habenula, the stria medullaris and the pineal body. ... The prethalamus (formerly described as ventral thalamus) or subthalamus is part of the diencephalon and therefore part of the brain. ... The zona incerta is a small region of gray matter that is part of the subthalamus. ... Ontogeny (also ontogenesis or morphogenesis) describes the origin and the development of an organism from the fertilized egg to its mature form. ...


Phylogenetic modifications are such that this article essentially deals with the human thalamus and may differ in comparison with accounts in non-upper primate species. In normal humans, the two thalami are prominent bulb-shaped masses, about 5.7 cm in length, located obliquely (about 30°) and symmetrically on each side of the third ventricle. The two can adhere on a variable extent in 30% of humans. This adhesio interthalamica (interthalamic adhesion, or massa intermedia) does not contain interthalamic neural connection in our species. The medial surface of the thalamus constitutes the upper part of the lateral wall of the third ventricle, and is connected to the corresponding surface of the opposite thalamus by a flattened gray band, the Interthalamic adhesion (massa intermedia, middle commissure, gray commissure). ...


Anatomy

The thalamus comprises a system of lamellae (made up of myelinated fibers) separating different thalamic subparts. Other areas are defined by distinct clusters of neurons, such as the periventricular gray, the intralaminar elements, the "nucleus limitans", and others. These latter structures, different in structure from the major part of the thalamus, have been grouped together into the allothalamus as opposed to the isothalamus (Percheron, 2003).[1] This distinction simplifies the global description of the thalamus. Myelin is an electrically insulating phospholipid layer that surrounds the axons of many neurons. ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... Drawing by Santiago Ramón y Cajal of neurons in the pigeon cerebellum. ... The Allothalamus is a division used by some researchers in describing the thalamus. ... The Isothalamus is a division used by some researchers in describing the thalamus. ...


Isothalamus

The isothalamus constitutes 90% or more of the thalamus, and despite the variety of functions it serves, follows a simple organizational scheme. The constituting neurons belong to two different neuronal genera. The first correspond to the thalamocortical neurons (or principal). They have a "tufted"(or radiate) morphology, as their dendritic arborisation is made up of straight dendritic distal branches starting from short and thick stems. The number of branches and the diameter of the arborisation are linked to the specific system of which they are a part of, and to the animal species. They have the rather rare property of having no initial axonal collaterals, which implies that one emitting thalamocortical neuron does not send information to its neighbor. They send long-range glutamatergic projections to the cerebral cortex where they end electively at the layer IV (or around) level. The other genus is made up of "microneurons". These have short and thin dendrites and short axon(s) and thus belong to local circuitry neurons. Their percentage in comparison to thalamocortical neurons varies across species, highly increasing with evolution. Their short axonal parts contact thalamocortical or other local circuitry neurons. Their neurotransmitter is GABA. The dendrites of the two constituting genera receive synapses from a variety of afferent axons. The connection back to the thalamocortical neurons create "triads" modulating the thalamocortical output. One subcortical afference comes from the perithalamus (reticulate nucleus). This receives axonal branches from thalamocortical neurons. Its afferences are also GABAergic. The number of perithalamic neurons strongly decreases in evolution in opposition to the large increase in microneurons (Arcelli et al. 1997).[2] To some extent the perithalamus plays a role in the local circuitry. The circuitous connection with corticothalamic neurons participates in the elaboration of thalamic rhythms. The different functional modalities represented in the thalamus are segregated in specific anatomical regions, differentiated by the cerebral systems from where they receive their afferent projections. There are more corticothalamic than thalamocortical axons. Corticothalamic endings are of two kinds. The "classical" projection emanates from layer VI of the cortex,the axons are thin and have a long, almost straight, trajectory through the thalamus, not respecting intrathalamic borders. They emit only short perpendicular collaterals (the arborization formin a thin cylinder (Globus and Scheibel). Their terminal synapses are glutamatergic. The second kind of corticothamic axons is the Rockland type II (1994).[3] This emanates from larger pyramidal cells and is much thicker. Its ending is small, dense and globular. Its synapses are located close to the soma of the thalamic neuron, often forming the center of glomerular complexes. The isothalamus serves the function of transforming and distributing "prethalamic" information to the cortex. Dendrites (from Greek dendron, “tree”) are the branched projections of a neuron that act to conduct the electrical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project. ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... Glutamate is the anion of glutamic acid. ... Location of the cerebral cortex Slice of the cerebral cortex, ca. ... Gaba may refer to: Gabâ or gabaa (Philippines), the concept of negative karma of the Cebuano people GABA, the gamma-amino-butyric acid neurotransmitter GABA receptor, in biology, receptors with GABA as their endogenous ligand Gaba 1 to 1, an English conversational school in Japan Marianne Gaba, a US model... Illustration of the major elements in a prototypical synapse. ... Glutamate is the anion of glutamic acid. ...


Arterial supply

The thalamus derives its blood supply from a number of arteries including polar and paramedian arteries, inferolateral (thalamogeniculate) arteries, and posterior (medial and lateral) choroidal arteries.[4] These are all branches of the posterior cerebral artery. The arterial circle and arteries of the brain. ...


Function

The thalamus is known to have multiple functions. Deduced from the design of the isothalamus, it is generally believed to act as a translator for which various "prethalamic" inputs are processed into a form readable by the cortex. The thalamus is believed to relay information selectively to various parts of the cortex, as one thalamic point may reach one or several regions in the cortex.


The thalamus also plays an important role in regulating states of sleep and wakefulness. Thalamic nuclei have strong reciprocal connections with the cerebral cortex, forming thalamo-cortico-thalamic circuits that are believed to be involved with consciousness. The thalamus plays a major role in regulating arousal, the level of awareness and activity. An animal with a severely damaged or severed thalamus suffers permanent coma. Sleep is the state of natural rest observed in humans and throughout the animal kingdom, in all mammals and birds, and in many reptiles, amphibians, and fish. ... Consciousness is a quality of the mind generally regarded to comprise qualities such as subjectivity, self-awareness, sentience, sapience, and the ability to perceive the relationship between oneself and ones environment. ... In medicine, a coma (from the Greek koma, meaning deep sleep) is a profound state of unconsciousness. ...


Many different functions are linked to the system to which thalamic parts belong. This is at first the case for sensory systems (which excepts the olfactory function) auditory, somatic, visceral, gustatory and visual systems where localised lesions provoke particular sensory deficits. A major role of the thalamus is devoted to "motor" systems. This has been and continues to be a subject of interest for investigators. VIm, the relay of cerebellar afferences, is the target of stereotactians particularly for the improvement of tremor. The role of the thalamus in the more anterior pallidal and nigral territories in the basal ganglia system disturbances is recognized but still poorly known. The contribution of the thalamus to vestibular or to tectal functions is almost ignored. The thalamus has been thought of as a "relay" that simply forwards signals to the cerebral cortex. Newer research suggests that thalamic function is more complicated.[5] The auditory system is the sensory system for the sense of hearing. ... Wikipedia does not yet have an article with this exact name. ... A term often used in usability enginering or user interface design Often conected with the Emotional feelings in a product signifies the WOW feeling when seeing a new product. ... Taste is one of the most common and fundamental of the senses in life on Earth. ... The visual system is the part of the nervous system which allows organisms to see. ... For the film see Tremors (film). ... The pallidum (Latin for pale) is a sub-cortical structure of the brain. ... The substantia nigra, (Latin for black substance, Soemering) or locus niger is a heterogeneous portion of the midbrain, separating the pes (foot) from the tegmentum (covering), and a major element of the basal ganglia system. ... The basal ganglia (or basal nuclei) are a group of nuclei in the brain interconnected with the cerebral cortex, thalamus and brainstem. ...


Pathology

Cerebrovascular accidents (strokes) can cause thalamic syndrome (Dejerine and Roussy, 1906),[6] which results in a contralateral hemianaesthesia, burning or aching sensation on one half of a body (painful anaesthesia), often accompanied by mood swings. Ischaemia of the territory of the paramedian artery, if bilateral, causes serious troubles including akinetic mutism accompanied or not by oculomotor troubles. Stroke (or cerebrovascular accident or CVA) is the clinical designation for a rapidly developing loss of brain function due to an interruption in the blood supply to all or part of the brain. ... A mood disorder is a condition whereby the prevailing emotional mood is distorted or inappropriate to the circumstances. ...


Korsakoff's Syndrome, stems from mammillary bodies, mammilothalamic, or thalamic lesions. Korsakoffs syndrome (Korsakoffs psychosis, amnesic-confabulatory syndrome), is a degenerative brain disorder caused by the lack of thiamine (vitamin B1) in the brain. ...


Development

The thalamic complex is composed of the perithalamus (or prethalamus, previously also known as ventral thalamus), the zona limitans intrathalamica (ZLI) and the thalamus (dorsal thalamus).[7][8] The zona limitans intrathalamica (ZLI) is a transverse boundary located between the prethalamus (previously also known as ventral thalamus) and the functional distinct thalamus (dorsal thalamus ). Besides its morphological characteristics, it bears the hallmarks of a signalling centre. ...


The ZLI is a transverse boundary located between the perithalamus and the functional distinct thalamus. Besides its morphological characteristics, it bears the hallmarks of a signalling centre. Fate mapping experiments in chick have shown that the ZLI is cell lineage restricted at its boundaries and therefore can be termed a true developmental compartment in the forebrain.[9]


Besides morphological characteristics, the ZLI is the only structure in the alar plate of the neural tube that expresses signaling molecules.[10]


In mouse, the function of Shh (Sonic Hedgehog) signaling at the ZLI has not been addressed directly due to a complete absence of the diencephalon in Shh mutants.[11] Sonic hedgehog homolog (SHH) is one of three proteins in the mammalian hedgehog family, the others being desert hedgehog (DHH) and Indian hedgehog (IHH). ...


Studies in chicks have shown that Shh is both necessary and sufficient for thalamic gene induction.[12]


In zebrafish, it was shown that the expression of two Shh genes, shh-a and shh-b (formerly described as twhh) mark the ZLI territory, and that Shh signaling is sufficient for the molecular differentiation of both the prethalamus and the thalamus but is not required for their maintenance and Shh signaling from the ZLI/alar plate is sufficient for the maturation of prethalamic and thalamic territory while ventral Shh signals are dispensable.[13] The name zebrafish applies to several different kinds of fish with striped bodies considered to resemble a zebra: Brachydanio rerio, also called Danio rerio or the Zebra Danio, is a commonly used model organism in studies of biological development. ...


References

  1. ^ Percheron, G. (2003) "Thalamus". In Paxinos, G. and May, J.(eds). The human nervous system. 2d Ed. Elsevier. Amsterdam. pp.592-675
  2. ^ Arcelli P, Frassoni C, Regondi M, De Biasi S, Spreafico R (1997). "GABAergic neurons in mammalian thalamus: a marker of thalamic complexity?". Brain Res Bull 42 (1): 27-37. PMID. 
  3. ^ Rockland K (1994). "Further evidence for two types of corticopulvinar neurons". Neuroreport 5 (15): 1865-8. PMID. 
  4. ^ Percheron, G. (1982) The arterial supply of the thalamus. In Schaltenbrand and Walker, A.E.(eds) Stereotaxy of the human brain. Thieme . Stuttgart. pp.218-232
  5. ^ http://www.livescience.com/humanbiology/060817_brain_boot.html
  6. ^ Dejerine, J. and Roussy. G.(1906) Le syndrome thalamique. Rev. Neurol. 14: 521-532
  7. ^ Kuhlenbeck, H. (1937). The ontogenetic development of diencephalic centres in the bird's brain (chick) and comparison with the reptilian and mammalian diencephalon. J. Comp. Neurol. 66
  8. ^ Shimamura, K., Hartigan, D. J., Martinez, S., Puelles, L. and Rubenstein, J. L. (1995). Longitudinal organization of the anterior neural plate and neural tube. Development 121,3923 -3933.
  9. ^ Zeltser, L. M., Larsen, C. W. and Lumsden, A. (2001). A new developmental compartment in the forebrain regulated by Lunatic fringe. Nat. Neurosci. 4, 683-684.
  10. ^ Puelles, L. and Rubenstein, J. L. (2003). Forebrain gene expression domains and the evolving prosomeric model. Trends Neurosci. 26,469 -476.
  11. ^ Ishibashi, M. and McMahon, A. P. (2002). A sonic hedgehog-dependent signalling relay regulates growth of diencephalic and mesencephalic primordia in the early mouse embryo. Development 129,4807 -4819.
  12. ^ Kiecker, C. and Lumsden, A. (2004). Hedgehog signalling from the ZLI regulates diencephalic regional identity. Nat. Neurosci. 7,1242 -1249.
  13. ^ Scholpp S, Wolf O, Brand M, Lumsden A. Hedgehog signalling from the zona limitans intrathalamica orchestrates patterning of the zebrafish diencephalon'. Development. 2006 Mar;133(5):855-64[1]

See also

The basal ganglia system is a pair and symmetrical major cerebral system that has only recently been recognized. ... // medulla oblongata medullary pyramids pons paramedian pontine reticular formation fourth ventricle cerebellum cerebellar vermis cerebellar hemispheres anterior lobe posterior lobe flocculonodular lobe cerebellar nuclei fastigial nucleus globose nucleus emboliform nucleus dentate nucleus tectum inferior colliculi superior colliculi mesencephalic duct (cerebral aqueduct, Aqueduct of Sylvius) cerebral peduncle midbrain tegmentum ventral tegmental... There are very few or no other articles that link to this one. ... Nuclear groups of the thalamus include: anterior nuclear group anteroventral nucleus anterodorsal nucleus anteromedial nucleus medial nuclear group dorsomedial nucleus parvocellular part magnocellular part midline nuclear group paratenial nucleus parventricular nucleus reuniens nucleus rhombodoidal nucleus intralaminar nuclear group centromedian nucleus parafascicular nucleus paracentral nucleus central lateral nucleus central medial nucleus...

Additional images

External links


  Results from FactBites:
 
Thalamus - Wikipedia, the free encyclopedia (1501 words)
The thalamus (from Greek θαλαμος = bedroom, chamber) is an element of the brain (part of the central nervous system contained in the skull, in front of the cerebellum).
Due to different ontogenetic origins, two diencephalic elements must be distinguished from the thalamus proper: the epithalamus (comprising mainly the habenula) and the perithalamus (past ventral thalamus and "reticulate nucleus") separated from the thalamus by the lamella lateralis.
The thalamus is largely made of nuclear groups that relate to specific functions in the brain (see List of thalamic nuclei).
  More results at FactBites »

 
 

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